The present invention is drawn to an automotive ignition coil tester for the identification of coils that have failed and coils which are about to fail.
Spark ignition systems are used extensively in most small and intermediate size engines, such as those used in automotive applications. A spark ignition system is used to provide a spark in the cylinders of both two and four cycle engines to ignite the compressed air-fuel mixture to drive the pistons (or, in the case of a rotary engine, the rotors). The ignition system uses a battery and a generator to supply electrical power to the system, and a distributor having points or a breakerless impulse generation system, which together are used to supply ignition pulses to spark plugs located in each of the cylinders. The heart of the ignition system is the ignition coil, which is located between the power supply and the distributor. The ignition coil converts the low voltage of the power supply (the battery) to the high voltage pulses required by the spark plugs.
If an ignition coil fails, the engine will be inoperative. As such, it is desirable to have some mechanism for testing an ignition coil to determine whether or not it is good or defective. While an ohmmeter may be used with limited success to check a coil to see whether it is defective, an ohmmeter does not test a coil under actual operating conditions. In use, an ohmmeter is used to check if the resistance falls within a given range. If it does it is assumed that the coil is not defective.
However, it is possible for coils to “ohm out” with an acceptable resistance and still be defective, that is, it may fail in the immediate future or under operating conditions. This creates an exasperating situation in which an automotive mechanic falsely believes that the problem cannot be due to a defective oil, because it ohms out properly, and therefore spends a great deal of time investigating and possibly even replacing other properly functioning component parts until all else has been exhausted. Finally in desperation, the mechanic may decide to replace the coil which then solves the problem. As a result of a faulty test of the coil, a great deal of time is spent troubleshooting and attempting repair in vain. Additionally, if such a faulty coil is not detected, the consumer drives the vehicle away only to have the coil fail later.
Because a bad coil is often a cause of ignition problems even when it “ohms out” properly, many mechanics replace older coils as a matter of course when dealing with ignition problems. As such, many properly-functioning coils are unnecessarily replaced at significant expense to vehicle owners.
In addition to the ohmmeter test, many ignition coil testers have been developed that attempt to test the coil under operating conditions to see if it properly produces a spark or a facsimile thereof. While these systems can be useful for identifying bad coils, they do not always identify coils that are malfunctioning intermittently and cannot identify coils that are about to fail. Clearly, it is desirable to be able to easily and quickly ascertain with accuracy whether a coil is functioning properly, about to fail, or has already failed.
As might be expected, the prior art contains a number of references which, to some extent, have attempt to address at least part of this problem. U.S. Pat. No. 2,249,157, to Morgan et al., U.S. Pat. No. 3,354,387, to Whaley et al., and U.S. Pat. No. 4,186,337, to Volk et al. are three such references. The Morgan et al. patent uses a large device with electrical circuitry to supply pulses to a coil and to analyze the output. In operation, the Morgan et al. device uses a complex and bulky electrical apparatus to merely determine visually whether the secondary coil has produced an output. It will not necessarily identify intermittent failures since visual indications of intermittent failure can be difficult to ascertain. Furthermore, Morgan et al. cannot determine if a coil is likely to fail in the near future.
The Whaley et al. patent is an improvement over Morgan et al. in that it is smaller, but still uses a visual indication of the spark. Again, however, it will not necessarily identify intermittent failures and cannot determine if a coil is about to fail.
The Volk et al. patent is concerned with testing the entire ignition system and thus has many other parts and functions. For isolated testing of the coil, it sends a substitute pulse (e.g., that a good ECU would supply) to the coil and checks for function with a spark indicator device. The spark indicator device provides both audio and visual feedback, but it cannot identify when a coil is about to fail.
U.S. Pat. No. 4,331,921 to Walker discloses a circuit for detecting an interruption of primary current caused by other ignition system problems. U.S. Pat. No. 4,401,948, to Miura et al. discloses a system measuring the rise of secondary coil output voltage to determine stray capacitance in the ignition system. U.S. Pat. No. 4,449,100 to Johnson et al. discloses a device which evaluates the integral of secondary voltage over time. These devices are complex, for the most part expensive, and are not designed to determine whether a coil is functioning properly or not, or whether it is about to fail.
U.S. Pat. No. 5,196,798, to Baeza et al. is designed to test coil function. However, it appears that Baeza et al. only supplies a maximum of 12 volts to the coil being tested. Since coils generally need an extra “kick” to get started, Baeza et al. does not fire the coil being tested under operating conditions. As with many of the other testers, the device of Baeza et al. uses a visual indicator to indicate function, an electrode spark gap viewable through a window, and is thus subject to the difficulties of identifying intermittent problems. The coil tester of Baeza et al., despite being described as inexpensive, also requires additional elements such as a resistor for use with coils requiring an external resistor for proper operation, a short circuit detection circuit, a short circuit indicator lamp, a vacuum, and a spark gap viewer.
U.S. Pat. No. 6,836,120 to Lite discloses another ignition coil tester. This unit relies upon a visual confirmation of a spark, but only tests with a single pulse. One pulse is not accurate enough to be efficient, or to find potential intermittent problems. Lite attempts to identify weak or failing coils by use of a variable spark gap. However, this can be more a measure of the power supply (i.e., vehicle battery) than the function of the coil. As admitted by Lite, spark generation is also affected by the atmosphere within the spark chamber, which is difficult to keep consistent due to the need for a variable length electrode within the chamber.
U.S. Pat. No. 5,479,101 to Change discloses another ignition coil tester. This unit needs an external power supply (i.e., 110V AC from a wall) and further includes short circuit and open circuit detectors and indicators. A series of neon lamps is used to indicate the strength of the coil output.
Published App. No. US 2005/0200361 to Bumen discloses an ignition coil tester that uses a fake cylinder chamber to view the spark. It uses the vehicle's ignition system and tests the coil as if it were in its installed state. The coil goes into the chamber and is fired using a fake spark plug. The Bumen device is expensive and, since coils vary in size and shape, a new test chamber would have to be built for any additional coils.
GB Pat. No. 1190438 to Ledger et al. discloses a tester comprising an electric motor, a set of points, and a condenser for the testing of conventional coils using an adjustable, calibrated spark gap. It apparently relies upon visual inspection of the spark, and thus suffers the problems mentioned above.
U.S. Pat. No. 2,501,802 to Walker discloses an ignition coil tester that uses a mechanical relay. It also relies upon visual inspection of the spark, and thus suffers the problems mentioned above.
While hobbyists have designed various circuits that use timing chips and automotive ignition coils to provide high voltage sparks or pulses, such as for flashing xeon tubes or making a “Jacob's Ladder” device, they do not disclose circuits or devices for testing ignition coils and identifying those that are failing or about to fail.
It is accordingly an aspect of the present invention to provide a small, inexpensive ignition coil tester which is capable of accurately testing an ignition coil to determine whether or not it has failed or is about to fail. The testing device should be simple, easy to use, and provide direct connections to an automotive type coil so that it may be tested.
It is an aspect of the invention to provide an ignition coil testing device operable using electrical power from an automotive battery rather than requiring internal batteries in the device or other outside power sources, thus minimizing the size and weight of the testing device.
It is another aspect of the present invention to dispense with reliance on visual spark indicators by providing audio feedback of the coil being tested.
It is yet another aspect of the present invention to provide a test method for ignition coils that relies upon listening to coil operation to more reliably identify intermittent misses.
It is a further aspect of the to provide brief operation of a coil at its peak output to identify coils that are near failure.
It is another aspect of the invention to provide an ignition coil tester with a direct connection to coils so as to eliminate polarity errors during testing.
It is yet another aspect of the invention to provide an ignition coil tester using inexpensive and easily available parts.